The present invention generally relates to an air-conditioning system and more particularly to an air-conditioning system which avoids disturbances in operation which result from running an air-conditioning system when a passenger compartment of a vehicle is open to the atmosphere.
Vehicles are frequently equipped with an air-conditioning system which supplies an air current of a controllable temperature to a passenger compartment of the vehicle. The air-conditioning system controls the temperature of the air current, i.e. blow-out temperature, such that a deviation of an interior temperature of a passenger compartment of the vehicle determined by an interior temperature sensor from a given desired temperature becomes minimal, i.e. interior temperature control. This type of an air-conditioning system is part of an air-conditioning unit described in German Patent Specification (DE-P) 38 36 991.5.
In this case, the interior temperature sensor is frequently integrated in a control apparatus for the air-conditioning system which is arranged in a control panel of the vehicle. This interior temperature sensor is housed there in a small forced-ventilation duct which is open in the direction of the passenger compartment of the vehicle.
However, vehicles of this type, in addition to having a closed construction with a firm roof, are also built in an open or openable construction, i.e. convertible. When this type of a convertible vehicle is driven with an open roof, disturbances may occur in the air-conditioning system, such as excessive blow-out temperatures of the air flowing out of blow-out devices of the air-conditioning system into the passenger compartment of the vehicle, if the interior temperature sensor, as the result of unfavorable air flows or turbulences, is acted upon by cold ambient air.
It is therefore an object of the invention to provide an air-conditioning system of the initially mentioned type which avoids the mentioned disturbances when the vehicle is open.
The principal advantages provided by advantageous embodiments of the present invention include that, by means of simple measures, an effective air-conditioning system is provided for a vehicle with closable body openings which ensures the comfort in the passenger compartment of the vehicle when the vehicle body openings are closed as well as when they are open and particularly avoids an excessive blow-out temperature of the air flowing into the passenger compartment of the vehicle.
For this purpose, according to one embodiment of the present invention, a switching device is provided in the vehicle which detects a condition of an open vehicle body opening and, in this condition, causes a switching-over of the air-conditioning system from an interior temperature control mode to a blow-out temperature control mode. In this embodiment, the switching device is constructed as a switch which is to be operated manually or as a limit switch which is actuated by a component closing the vehicle body opening
Since frequently another switching input cannot simply be added to (electronic) control apparatuses of air-conditioning systems of existing vehicles, it is also possible, according to a further embodiment of the invention, to implement the switching device as a software or firmware module. This arrangement detects the condition of the opened or closed vehicle from sensor signals by determining, from the blow-out temperature and at least the rotational speed stage of a blow-out fan of the air-conditioning system or the vehicle speed or the outside temperature, a limit value for a time variation of a temperature deviation of an interior temperature (ti) from a desired temperature (ts) (minimum desired variation) and comparing this limit value with a time variation of the temperature deviation of the interior temperature from the desired temperature. When there is a variation of a shorter duration than the minimum desired variation, the air-conditioning system is switched from the interior temperature control mode to the blow-out temperature control mode.
Preferably, the comparison takes place only at blow-out temperatures which are in higher temperature ranges. The switching between the two control modes will be caused only if the time variation of the temperature deviation is less than the minimum desired variation for at least a given time period. In this embodiment, when the blow-out temperature is controlled, a desired value for the blow-out temperature is virtually increased by a fixed amount.
According to yet another embodiment of the invention, it is also conceivable to monitor the interior temperature measured by the interior temperature sensor with respect to its time variation and to switch the air-conditioning system from the interior temperature control mode to the blow-out temperature control mode, if the measured interior temperature is subjected to strong time fluctuations. In this case, the switching over should again take place only at a blow-out temperature in a higher temperature range and only if the strong time fluctuations of the measured interior temperature occur for at least a given time period.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.